Phonograph records are made by impressing information into the grooves with a mechanism that is always held perpendicular to a radial line on the record. Accurate reproduction is thus achieved by keeping the stylus/cantilever axis on the playback cartridge in the same orientation. But this has been very hard to do at a reasonable cost.
Prior art record players that use a simple, low cost, pivoted tone arm carry the cartridge through an arcuate path across the record. The cartridge continuously changes its angular position relative to the groove radius: this is unacceptable for high fidelity sound reproduction and therefore higher cost turntables often use linear tracking schemes. These actually shift the pivot point of the tone arm so as to keep the arm more or less tangent to the grooves. But even these complicated and expensive devices do not track perfectly because, before they can correct the tracking, they must let the error become large enough to accommodate eccentric spindle holes and the marked spiral nature of the inner grooves. In addition, they usually correct only in the forward direction. My invention avoids these problems.